This invention relates to improvements in apparatus and methods of producing filament wound tubular products, and more particularly to a method and apparatus for applying longitudinal reinforcing to continuously generated plastic pipe.
In the manufacture of continuously generated plastic pipe, such as resin-impregnated fiber pipe of the type disclosed in U.S. Carter Pat. No. 3,700,519; Oct. 24, 1972, and U.S. Carter Pat. No. 4,053,343; Oct. 11, 1977, both assigned to the same assignee as the present invention, thermosetting resin-coated continuous fiber elements, such as glass rovings, are wound circumferentially onto a conveyor tube. The tube is rotated on a mandrel and continuously advanced in an axial direction. Normally, several winding stations are employed to build layers of resin-impregnated fibers upon the conveyor tube. Pipe so produced generally has high circumferential strength, but the axial strength is low due to the absence of longitudinally extending fibers in the pipe. Accordingly, additional steps must be taken to provide the required longitudinal reinforcing.
Applying longitudinal reinforcing in fiber wound plastic pipe has always been more difficult and costly than circumferential reinforcement. One manner of longitudinally reinforcing plastic pipe is to apply a fiber reinforced tape longitudinally to the pipe during the winding process. This is costly and unduly complicates the manufacture of the pipe.
Another method of applying longitudinal reinforcing fibers to sections of pipe being produced by the lathe method is disclosed in U.S. Goerden et al Pat. No. 3,791,900; Feb. 12, 1974. There, resin-impregnated fiber rovings being circumferentially wound onto a rotating mandrel pass over a pair of spaced rollers prior to being wound onto the pipe. Additional fiber rovings supplied through a reciprocating guide moving transverse to the direction of movement of the circumferential fibers are deposited onto the layer of circumferential fibers passing over the rollers. The additional fibers are deposited at a rate greater than the rate at which the circumferential fibers are being wound onto the pipe as loops or coils, disposed generally in a longitudinal direction, to form a resin-impregnated mat which is carried on the supporting layer of circumferential fibers and wound onto the pipe therewith. This technique does not permit precise control of the deposition of the longitudinal reinforcing.